In a magnetic disk apparatus, when an amount of an offtrack of a magnetic head from the target track in the radial direction exceeds a predetermined value during data recording, there is the possibility that a part of the data of the neighboring track is erased and the information of the neighboring track cannot be read.
In a conventional magnetic disk apparatus using an embedded servo system including a data recording area and servo information for a recording track on a magnetic disk medium, a track position signal is demodulated from reproduced servo information during data writing and writing in the state of offtrack is prevented by monitoring the amount of offtrack during writing. Namely, an art for prohibiting the write operation is used when the amount of offtrack of the magnetic head in the direction of track width immediately before writing or during writing is more than a preset value.
The present invention relates to a magnetic disk apparatus for positioning a magnetic head for a recording track provided on a circular magnetic disk medium and recording information on it.
When the servo quality is high and the sampling cycle is very short, the aforementioned art is effective as an offtrack writing prevention means. However, in a magnetic disk apparatus using the embedded system having no dedicated servo surface and having servo information on the data surface, the location for storing servo signals is limited so as to reserve as many data recording areas as possible and as a result, it is hard to shorten the sampling cycle. Also with respect to a servo signal recorded on a magnetic disk medium, due to effects of vibration during writing of the servo signal, a medium defect, noise, and others, the quality thereof is not always sufficiently high and it is hard to make the specified value for monitoring a write position error sufficiently smaller.
With respect to the reliability of written data, when tracks A, B, and C are lined up side by side, the track A is shifted toward the track B and already written, and the track B is shifted toward the track C and already written, and if, when the track C is to be written, it is shifted toward the track B and written, the state of reproducing the data of the track B is a most severe condition. Therefore, to maintain the reliability, even in a case of combination of the aforementioned worst position errors, it is necessary to reserve the recorded data and it is a condition that the occurrence frequency is very low on a probability basis, so that it is requested to set the specified value for monitoring a position error to a more smaller value.
However, when the specified value for monitoring a position error is set to an extremely small value, write suspension (write fault) occurs frequently and there is the possibility that the equipment performance lowers and a malfunction of write inhibit is caused.
On the other hand, in correspondence with an increase in the recording capacity requested to a magnetic disk apparatus at present and to realize a decrease in cost, it is essential to improve the recording density and it is necessary to narrow the track pitch equivalent to the density in the radial direction on a magnetic disk medium. On a magnetic disk whose track pitch is minimized, the condition for positioning the magnetic head in the direction of track width becomes severe more and more.
The present invention is realized in consideration of such a problem of the prior art and an object of the present invention is to provide a magnetic disk apparatus for making the offtrack of the recording track smaller without sacrifice of the access speed and improving the reliability by reducing the occurrence probability of write fault at the same time.
According to the present invention, the above object is accomplished by detecting a position error of the magnetic head in the direction of track width on a magnetic disk medium by a plurality of threshold values, typically two threshold values and when it is decided that a position error which may cause a failure depending on the state of position error when data is written on the neighboring track, though it is not fatal, is caused (write warning), by writing the data as it is on the track causing offtrack, temporarily write-inhibiting the track neighboring to the track, reading the information written on the track causing the offtrack later when the equipment is in the state of idle, and rewriting the information on another track.
Namely, the magnetic disk apparatus of the present invention comprises a magnetic disk medium having tracks arranged concentrically or spirally, a magnetic head for recording or reproducing for the tracks, a detection means for detecting position information of the magnetic head in the direction of track width during recording, a decision means for deciding the magnitude of a position error of the magnetic head in the direction of track width using the position information and a plurality of threshold values, and a means for limiting the later recording position according to the decision result by the decision means.
The limitation of recording position according to the decision result by the decision means is to temporarily inhibit writing data, for example, when it is decided by the decision means at the time of recording data on a preset track that the amount of offtrack is larger than a preset threshold value, on the whole or a part of one track on both sides neighboring to the track.
When it is decided by the decision means that the amount of offtrack when data is written on the preset track last is larger than the preset threshold value, the data of the track is rewritten on another track so as to maintain the data.
The magnetic disk apparatus of the present invention has a track information table for registering, when it is decided by the decision means that the amount of offtrack when data is written on the preset track last is larger than the preset threshold value, the track as a track requiring rewriting and temporarily registering the track neighboring to the track as a write inhibit track.
Furthermore, the magnetic disk apparatus has a logical-physical address conversion table for converting the logical address of a data write or read instruction from a host device to a physical address on the magnetic disk medium and a means for changing the logical-physical address conversion table at any time.
When it is decided by the decision means that the amount of offtrack when the data is rewritten on the rewritten track is smaller than the preset threshold value, that is, the rewriting succeeds and the data is completely recorded, the means for changing the logical-physical address conversion table at any time updates the logical-physical address conversion table and corresponds the physical address of the rewritten track to the logical address of the track requiring rewriting.
The aforementioned rewrite is executed when the write or read instruction from the host device is monitored, and the instruction is not issued, and the operation by an instruction from the host device is not necessary.
Typically, when the amount of position error PE meets the condition of Ewf greater than PE greater than =Eww for two threshold values Ewf and Eww meeting Ewf greater than Eww, the decision means registers the track in the track information table as a track requiring rewrite and temporarily write-inhibits the tracks on both sides neighboring to the track.
Or, when the amount of position error PE meets the condition of Ewf greater than PE greater than =Eww for two threshold values Ewf and Eww meeting Ewf greater than Eww, the decision means registers the track in the track information table as a track requiring rewrite and temporarily write-inhibits the track neighboring to the track in the direction of position error. However, in this case, it is necessary to know not only the magnitude of the amount of position error PE but also the direction of the position error.
According to the magnetic disk apparatus of the present invention, when the threshold value for monitoring a position error is set in a plurality of stages, typically 2 stages and the rewrite process by write warning is executed, it is possible to make the offtrack of the recording track smaller without sacrifice of the access speed. By doing this, the threshold value of write fault can be increased, and the occurrence probability of write fault reduces, and the reliability improves. At the same time, since the occurrence probability of write fault reduces, the frequency of retry reduces and the access speed during write improves. Furthermore, since the offtrack of the recording track becomes smaller, the error rate during read improves and the reliability and access speed improve.